1. Field of the Invention
The present invention relates generally to a communication system, and in particular, to an apparatus and method for efficiently allocating resources in uplink scheduling in a Broadband Wireless Access (BWA) communication system.
2. Description of the Related Art
Provisioning of services with diverse Quality of Service (QoS) levels at about high-speed to users is an active study area for the future-generation communication system. Particularly, active research is being conducted on the development of a new communication system that supports high-speed services by ensuring mobility and QoS to Wireless Local Area Network (WLAN) supporting relatively high data rates and Wireless Metropolitan Area Network (WMAN).
Institute of Electrical and Electronics Engineers (IEEE) 802.16a and IEEE 802.16e communication systems adopt Orthogonal Frequency Division Multiplexing/Orthogonal Frequency Division Multiple Access (OFDM/OFDMA) for the physical channels of the WMAN system in order to support a broadband transmission network. Because a physical channel signal is transmitted on a plurality of subcarriers in OFDM/OFDMA in the WMAN system, IEEE 802.16a and IEEE 802.16e enable high-speed data transmission, and are in effect, OFDM/OFDMA-Broadband Wireless Access (BWA) communication systems.
IEEE 802.16a considers only a single-cell structure with no regard to mobility of Subscriber Stations (SSs). In contrast, IEEE 802.16e supports the SS' mobility to the IEEE 802.16a communication system. For the IEEE 802.16e system to ensure the mobility of SSs in a multi-cell environment, the operations of the SS and the Base Station (BS) must be modified. Particularly, handover for the SS in the multi-cell structure is under active study. Hereinafter, a mobile SS will be referred to as an MS.
FIG. 1 illustrates the configuration of a conventional BWA communication system.
Referring to FIG. 1, the BWA communication system is configured in a multi-cell structure. Thus, it includes cells 100 and 150, a BS 110 that covers the cell 100, a BS 140 that covers the cell 150, and a plurality of MSs 111, 113, 130, 151 and 153. Signaling between the BSs 110 and 140 and the MSs 111, 113, 130, 151 and 153 is based on OFDM/OFDMA.
In OFDMA proposed for the BWA communication system, subchannels are composed of subcarriers that constitute one OFDM symbol, and a plurality of OFDM symbols form one frame.
FIG. 2 illustrates the structure of a data frame in the conventional BWA communication system. Particularly, the data frame is an Uplink (UL)/Downlink (DL) frame for an Orthogonal Frequency Division Multiple Access-Time Division Duplex (OFDMA-TDD) BWA communication system.
Referring to FIG. 2, the data frame is divided into a DL frame and a UL frame in time. A Transmit/receive Transition Gap (TTG) is interposed for transition from the downlink to the uplink and a Receive/transmit Transition Gap (RTG) is interposed for transition from the uplink to the downlink. The horizontal axis represents OFDMA symbol numbers and the vertical axis represents the logical numbers of subchannels.
On the downlink, a preamble resides in a Kth OFDMA symbol, for synchronization acquisition, and data information broadcast commonly to MSs such as a Frame Control Header (FCH) and a DL-MAP is located in a (K+1)th OFDMA symbol.
The preamble delivers a synchronization signal, i.e. a preamble sequence by which synchronization is acquired between a BS and an MS. That is, the preamble is required for the MS to acquire synchronization to data transmitted by the BS. The MS extracts the synchronization information from the preamble through its MODEM.
The FCH is composed of two subchannels, carrying basic information about subchannels, ranging and modulation. An analysis of the FCH reveals the size of the DL-MAP and the frequency reuse factor (referred to as reuse) of the BS, for example, reuse 1 or reuse 3.
The DL-MAP delivers a DL-MAP message. It has information required for data extraction and service provisioning to MSs, such as the positions and sizes of data in the DL frame. Therefore, data can be extracted from the DL frame by analyzing the DL-MAP information.
In (K+3)th through (K+15)th OFDMA symbols, Downlink bursts (DL bursts) are positioned, for example, DL burst #1 to DL burst #6. Data is extracted from the DL bursts based on general data information, such as information acquired from the DL-MAP.
On the uplink, Uplink bursts (UL bursts), UL burst #1 to UL burst #5 are located in (K+17)th to (K+26)th OFDMA symbols. A Ranging Subchannel also occupies the (K+17)th to (K+26)th OFDMA symbols. Data is extracted from the UL bursts based on general data information such as information acquired from an Uplink MAP (UL-MAP) delivered in DL burst #1.
Each subchannel is composed of a plurality of subcarriers. Depending on system situation, a number of subcarriers form one subchannel. As described above, the IEEE 802.16e OFDMA communication system configures subchannels each being a set of subcarriers according to system situation and allocates resources to a plurality of users (i.e. MSs) by the subchannels.
FIG. 3 illustrates traffic transmission in the conventional BWA communication system. Particularly, a BS 350 allocates uplink resources to, for example, an MS 320 that transmits traffic using the allocated resources.
Referring to FIG. 3, the BS 350 selects an MS (e.g. the MS 320) to allocate resources to from among MSs 310, 320 and 330 in its coverage area by a scheduling procedure. The BS 350 determines the amount of resources and a Modulation and Coding Scheme (MCS) for the MS 320. Also, the BS 350 determines the position of the resources by which the MS 320 will transmit data. This operation is repeated until all uplink resources are allocated.
After the scheduling is completed, the BS 350 broadcasts uplink scheduling information indicating the result of the scheduling in a UL-MAP message to all the MSs 310, 320 and 330 in the cell.
The MSs 310, 320 and 330 receive the UL-MAP message and, if resources have been allocated to them, transmit traffic at the positions of the allocated resources on the uplink. For example, if the UL-MAP message indicates the existence of resources allocated to the MS 320, the MS 320 transmits uplink traffic at the position of the allocated resources.
Basically, the BS seeks to maximize radio channel throughput and minimize the transmission delay of traffic in uplink scheduling. The BS aims to reduce interference with neighbor sectors, reduce UL-MAP overhead, expand cell coverage, reduce the power consumption of the MSs and maintain stable link performance between the BS and the MSs. Thus, the BS selects an operation algorithm that serves the above purposes. However, some objectives of the BS scheduling may be contradictory to one another. Hence, the scheduler of the BS attempts to fulfill the objectives appropriately according to their priority levels by adjusting parameters such as an MCS level preference and the amount of resources allocated per time.
Yet, there is no specified scheduling method and apparatus for satisfying the foregoing objectives in allocating uplink resources through frame-basis uplink scheduling in a broadband mobile communication system, particularly an OFDMA-TDD mobile communication system.